With the refinement in semiconductor technologies, non-volatile memories, for example, have been designed to be lighter in weight, achieve a higher-speed operation, and require less power consumption. As a result, the market for large-capacity non-volatile memory systems has significantly expanded, and information management in the large-capacity memory systems has become more important.
The refinement of non-volatile memories gradually increases variations in single devices, making it difficult to ensure the reliability of the memories. The variations, however, can be used to improve the security. The variations in non-volatile memory devices are determined by various factors a part of which is physical characteristics that are generated in a process, already determined in shipping, and hard to duplicate. For example, the smaller the area of a device becomes, the larger an influence of a single defect exerting on the device becomes. Examples of a technology for using an individual difference of a semiconductor device for authentication include, but are not limited to, a physical unclonable function (PUF).
The conventional security system that uses the variations in semiconductor devices, however, may possibly be inadequate.